1. Field of the Invention
The present invention relates generally to wireless terminals and more particularly to the mobility of addressing in wireless networks.
2. Description of Related Art
Wireless Broadband Access (“WBA”) based systems have been designed to have operational characteristics that are indistinguishable from Cable or DSL methods of broadband access from the viewpoint of the customer. However, wireless systems are subject to network termination resulting from signal fading and subscriber mobility and subscriber equipment may be connected to the network through any of multiple network termination points. In contrast, DSL Modems can connect to a single DSLAM along a single physical cable that is shielded against external noise and thus, DSL systems does exhibit fading or have multiple termination points. In cable systems, a shielded coaxial cable connects the modem to a CMTS and relatively minor fading occurs due to various factors. Even in a multiple CMTS system, every CMTS experiences similar levels of fading and a cable modem is typically redirected to its originally connected CMTS when a disconnection occurs.
Wireless systems may be viewed as multiple logical modems connected through different Network Termination points via different virtual cables, where the system is able to pick the best signal strength at the time that it is connected to an end-point. As time passes fading on the virtual cable causes the logical modem to disconnect from its current base station and the subscriber station directs the modem to reconnect based on best available signal strength. This behavior can be repeated many times. Fading may be apparently random or based on predictable patterns.
Customer premises equipment (“CPE”), such as a personal computer (“PC”), may respond to fading by disconnecting from the network. Upon reconnection, conventional systems generally assign a new IP address thereby causing shut-down all prior network connections in use by application in the CPE. Active connections, whether IP streaming or download in progress, have to be terminated and re-started using the newly-obtained IP address. Also, in many business uses, connections are made from the Internet to the CPE as well from the CPE to the Internet. For these connections, the CPE IP address must be advertised when changed. Even when a dynamic domain name service (“dynamic DNS”) method is implemented, DNS update can be a slow process, taking hours and sometimes days to propagate through the Internet.
For bridged base stations, the interaction of the base stations between which the subscriber connection transfers is significant. If the base stations are not in the same layer-2 network, then the latterly described problems apply. When the two base stations are within the same layer-2 network, the CPE need not change IP addresses and generally experiences a brief period of packet drop measurable in seconds. However, a new set of network topology problems will be observed. For example, any broadcast packet will be repeated over all connected base stations, potentially causing a broadcast storm. Malicious users could use broadcast storms to run theft of service and denial of service attacks. Furthermore, identification and debugging of network problems is made difficult.
The use of Dynamic VLANs may solve broadcast storm issues and may provide some IP address mobility. However, the initial IP address and VLAN assignment process can cause random distribution of IP addresses, resulting in an expanded and sometimes uncontrollable broadcast domain.